Ink jet inks must have a very low viscosity, typically less than about 20 centipoise at the jetting temperature. While hot melt inks have been used, liquid inks are generally more suited to high volume industrial printing. To achieve this low viscosity, liquid ink jet inks must either be aqueous or include a substantial amount of organic liquids. The low viscosity of ink jet inks also makes it more difficult to maintain a stable pigment dispersion. This problem may be avoided by using dyes that dissolve in the liquid medium, but it is advantageous to use pigment instead of dyes for other reasons, including lightfastness and permanency of the printing. However, the organic solvents that are employed in ink jet ink formulations to obtain stable pigment dispersions with good printing characteristics have to date included materials designated as hazardous air pollutants. The U.S. Federal 1990 Clean Air Act Amendments targeted certain compounds as hazardous air pollutants (HAPs) for special regulation. For example, the Amendments directed the EPA to establish emissions standards based on the use of “maximum achievable control technology” (MACT). While as yet only certain businesses are subject to the regulations, other businesses may wish to minimize or eliminate use of HAPs materials to avoid exposure to those materials.
Therefore, there is a need for an ink jet ink and an ink jet ink set for full-color printing (e.g., CMYK ink set) that avoids HAPs emissions during printing and yet has advantageous properties such as a viscosity suitable for ink jet printing, stable pigment dispersion, lightfastness, compatibility with industrial printer components, that can be printed on a wide range of substrates, and that can be printed with low maintenance (e.g., cleaning or replacing equipment). It is thus an object of the invention to provide an ink jet ink that is free of hazardous air pollutant compounds and a method of ink jet printing that does not release hazardous air pollutant emissions and provides these desirable ink characteristics.